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Insights Into the Stratigraphic Evolution of the Early Pennsylvanian Pocahontas Basin, VirginiaGrimm, Ryan P. 05 January 2011 (has links)
Early Pennsylvanian, coal-bearing, siliciclastic strata of the Breathitt Group within the Pocahontas Basin, southwestern Virginia, define a southeasterly thickening clastic wedge deposited in continental to marginal marine environments influenced by recurring, high-magnitude relative sea-level fluctuations and low-frequency changes in tectonic loading. A robust dataset of >1200 well logs, cores and numerous outcrops allowed a unique review of the Central Appalachian lithologic record during both the Late Paleozoic Ice Age and onset of the Alleghanian Orogeny.
The tropical depositional landscape produced stacked deposits of braided-fluvial channels, broad alluvial plains, tidally-influenced estuaries and small deltas. Trends in facies associations allowed development of a high-resolution sequence stratigraphic architecture based on regional flooding surfaces and bounding discontinuities. Analysis of vertical stacking patterns of lithofacies on regional cross-sections identified 15 widespread, unconformity-bounded depositional sequences with an average duration of ~80 kyr based on available geochronology.
Glacioeustatic control on stratigraphic architecture is supported by corresponding sequence duration within the short-eccentricity periodicity of the Milankovitch band, as well as the magnitude and extent of rapid facies shifts, suggesting that far-a-field variations in overall Gondwanan ice-sheet size and volume impacted base-level changes in the tropical basin. The progressive increase in magnitude of transgressions, as indicated by brackish-marine ichnofacies and other faunal indicators within regional high-frequency transgressive system tracts, indicate extrabasinal trends in ice-volume and eustasy.
High-frequency eustatic sequences are nested within four asymmetric composite-sequences, attributed to low-frequency variations in tectonic accommodation. Evidence for tectonic forcing on foreland-basin accommodation is based on abrupt facies shifts, angular stratal terminations and wedge-shaped composite-sequence geometries. Spatial and temporal trends in facies associations within composite-sequences reveal episodic variation in tectonic loading overprinted by recurring high-frequency eustatic events.
Petrology and detrital-zircon geochronology indicates that sediment was derived from low-grade metamorphic Grenvillian-Avalonian terranes and recycling of older Paleozoic sedimentary rocks uplifted as part of the Alleghanian orogen towards the southeast and, in part, from the Archean Superior Province to the north.
Applications of the observed facies distribution and petrophysics of these coal-bearing sedimentary rocks indicate numerous confining intervals within regional mudstones overlying coalbeds, suggesting the potential for beneficial geological storage of CO2 through enhanced-coal-bed-methane recovery. / Ph. D.
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Stratigraphic Architecture and Paleogeography of the Juniata Formation, Central AppalachiansBlue, Christina R. 06 May 2011 (has links)
Late Ordovician (Cincinnatian) strata of the central Appalachians provide an opportunity to study the effects of both tectonics and eustasy within a foreland-basin setting. The Juniata Formation consists of red sandstones, siltstones, and shales that were deposited as part of an extensive siliciclastic basin-fill that resulted from the Taconic Orogeny. This study attempts to resolve some of the questions regarding tectonic and eustatic influences on sedimentation by (1) reconstructing the paleogeographic environment of the Juniata Formation and (2) examining the stratigraphic architecture of the Juniata Formation. A combination of both outcrop and subsurface data was analyzed.
Seven facies were identified in this study, including: (1) "proto-vertisols", (2) red shale/mudstone, (3) siltstone/silty mudstone with interbedded sandstones, (4) quartz arenite and sublithic arenite, (5) argillaceous sandstone, (6) hummocky-bedded sandstones and siltstones, and (7) lithic sandstones and conglomerates. These facies are grouped into four facies associations (A–D), which are interpreted to be deposited from the inner shelf to the upper shoreface. Isopach and paleocurrent data suggest the shoreline was oriented NE–SW and detrital sediment was dispersed west and southwest across the basin.
Tectonics controlled the 2nd-Order basin-fill pattern, and these patterns vary along the strike of the basin. Eustatic changes are expressed in two 3rd-Order sequences that were identified in the formation, and possibly in the 4th-Order (?) cycles of Facies Association A. The Ordovician–Silurian boundary is expressed as an unconformity throughout the study area, and along-strike variations in the structural setting of the basin were important in its development. / Master of Science
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Characterization of Cu-mineralized carbonate veins in the Alta-Kvænangen Tectonic Window, NorwaySvens, Ellen January 2024 (has links)
The Alta-Kvænangen Tectonic Window is part of a regional greenstone belt that formed around 2.3 Ga – 2.0 Ga. The Bergmark anticline in the area has gone through greenschist to amphibolite facies metamorphism and hosts Cu, Co and Au mineralizations in hydrothermal veins, albite felsite and chemical traps. The area was mined during the late 19th century mostly in trenches but it has still got exploration potential. This project will classify carbonate veins that are hosted within two gabbro units, compare orientations between the barren and mineralized veins as well as discuss the origin of the veins. The study area has been affected by multiple extensional and compressional events during the Svecokarelian orogeny (1.9 – 1.8 Ga) and regional hydrothermal alterations including an influx of Na + Ca ± K ± Fe. Major shear zones were activated and used for transporting fluids which are thought to have controlled the formation of mineralization in second- or even third-order structures. The veins were studied using field work, detailed mapping, optical microscopy as well as scanning electron microscopy (SEM) and structural analysis. Results gave three different types of hydrothermal veins: 1) Fe oxide veins, 2) calcite veins and 3) dolomite-plagioclase-quartz veins. All of them show strong signs of deformation and recrystallization all while the chalcopyrite mineralization is heterogeneously distributed and commonly more or less bornite-altered. The veins pinch and swell over short distances and are sinuous but with a general orientation. Albite haloes are common for the veins but far from all veins have haloes. There are at least two generations of veins as some were found to have offset others. Brecciation, tension gashes and faults are also found in the area apart from veins. From the field measurements, two groups of orientations could be determined: one with a SW-NE direction and the other in NW-SE direction, both with relatively steep dips. Considering all downhole measurements, no conclusive results could be revealed, however, the optical televiewer results showed that the area has gone through a N-S compression giving a fold axis towards the west. In the end the orientations of the larger veins were found to either run parallel to the gabbro units or are connected to the NW-SE directed main brittle faulting in the Fennoscandian Shield. Smaller, surrounding veins having more diverse orientations. There are multiple signs of deformation and recrystallization in the mafic host rock but no fabric development can be seen. Its appearance varies locally depending on which alterations are dominating. It exhibits sodic-calcic, potassic and leucoxene alteration as well as albitization and carbonatization. The grain size varies from fine-grained to medium-grained which is more typical with a dolerite or basalt, even though it has been previously mapped as a gabbro. No pyroxene was found in the host rock and the plagioclase was Na-rich instead of the expected Ca-rich. The Bergmark anticline has multiple similarities with the Gällivare-Kiruna area in Sweden which include 1) high-temperature, low-pressure metamorphism resulting in regional alterations such as albitization, carbonatization, amphibole and magnetite alteration. 2) The mineralization consists of Cu, Co, Au, Fe and minor P. 3) The mineralization can be found disseminated in albite felsite, in chemical traps and in first to third order structures (e.g., faults or hydrothermal veins) in brittle, deformed rocks. 4) The mineralization is structurally controlled to the vicinity of major fault zones. 5) In both places, greenstone belts are important for the formation of mineralization. 6) Reactivation of brittle structures, similar to those in the Kiruna area during the second phase of subduction during the Svecokarelian orogeny (D2), is likely the cause for the veining in the Bergmark anticline. 7) A younger N-S compression is recorded in the area. Differences between the Bergmark anticline and the Gällivare-Kiruna area include the lack of intrusions in the vicinity to the Bergmark anticline.
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The Timing of Deformation in the Four Peaks Area, central Arizona, and relevance for the Mazatzal OrogenyMako, Calvin A 07 November 2014 (has links) (PDF)
The Mazatzal orogeny (1.66-1.60 Ga) is a key element of the tectonic evolution of the North American continent during the Proterozoic (Whitmeyer and Karlstrom, 2007). Recently, Mesoproterozoic detrital zircon grains (1.55-1.45 Ga) have been found in metasedimentary rocks that were thought to have been deformed during the Paleoproterozoic Mazatzal orogeny (Jones et al. 2011; Doe et al. 2012, 2013; Daniel et al. 2013). Some type examples Mazatzal deformation now seem to be too young to have been deformed in the accepted time of that orogeny (1.66-1.60 Ga) and may have been deformed in the younger, newly defined, Picuris orogeny. This leads to questions regarding the timing and nature of the Mazatzal orogeny and its importance in the evolution of the North American continent. The object of this research is to constrain the timing of deformation related to the Mazatzal and Picuris orogenies and clarify the Proterozoic history of the North American continent. The Four Peaks area in central Arizona has been selected as an ideal location to tightly constrain the timing of deformation. The area hosts a package of Proterozoic metasedimentary rocks that are folded into a kilometer-scale syncline, surrounded by vi Mesoproterozoic to Paleoproterozoic granitoids.
The Four Peaks syncline has been considered a type example of Mazatzal-age deformation (Karlstrom and Bowring, 1988). Zircon and monazite geochronology are presented along with structural and petrologic data in order to understand the geologic history of the Four Peaks area. The evidence suggests that three deformation events occurred at ~1675 Ma, 1665-1655 Ma and 1490-1450 Ma. Sedimentary deposition occurred 1665-1655 Ma and 1520-1490 Ma with a significant disconformity in between these episodes. Both the Mazatzal and Picuris orogenies can be associated with periods of deformation, sedimentary deposition and pluton emplacement. The most significant shortening event, which formed the Four Peaks syncline, occurred during Mesoproterozoic time and was related to the Picuris orogeny.
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Evolution of the continental crust and significance of the zircon record, a case study from the French Massif Central / L’évolution de la croute continentale vue par le zircon, résultats et limites de l’approche à partir de l’exemple du Massif Central françaisCouzinié, Simon 03 November 2017 (has links)
La formation de la croute continentale est une des conséquences majeures de la différenciation de la Terre. Les avancées récentes dans la compréhension de ce phénomène résultent de l’amélioration des techniques analytiques permettant la mesure in situ des compositions isotopiques en U-Pb-Hf-O de grains de zircon, minéral abondant dans les roches crustales. Cette étude reconstitue l’histoire du segment de croute affleurant dans l’est du Massif Central français (MCF), portion de la chaine Varisque d’Europe de l’Ouest, dans le but d’évaluer les limites d’utilisation des zircons pour retracer l’évolution crustale. L’origine et la signification géodynamique des principales unités lithologiques du MCF ont été étudiées en combinant les approches classiques de la pétrologie avec des données isotopiques U-Pb-Hf-O acquises sur zircon. Deux incohérences majeures existent entre nos résultats et les conclusions tirées de l’étude des zircons considérés hors de leur contexte pétrologique, approche généralement suivie pour analyser l’évolution crustale. Les âges modèles calculés à partir des données Hf suggèrent une importante croissance crustale au Mésoproterozoique dans le MCF, en contradiction avec le fait que 60% de la croute locale soit d’âge Néoproterozoïque. De plus, 5 à 10% de la croute du MCF a été formée durant l’orogènese Varisque sans que cela ne soit enregistré par le zircon. Dans les deux cas, ces incohérences résultent du caractère hybride des signatures isotopiques portées par les zircons. Celles-ci ne peuvent être correctement détectées et interprétées qu’en disposant de données pétrologiques complémentaires sur les roches contenant les grains analysés / The formation of the continental crust is a major consequence of Earth differentiation. Understanding how the crust formed and evolved through time is paramount to locate the vast mineral deposits hosted therein and address its influence on the global climate, ultimately affecting the development of terrestrial life. Recent advances on the topic of continental crust evolution benefited from improvements of analytical techniques enabling in situ measurements of U-Pb- Hf-O isotope compositions in zircon, a widespread accessory mineral of continental igneous rocks. The time constrains derived from the U-Pb chronometer coupled with the petrogenetic information retrieved from Hf-O isotope signatures are currently used to unravel the diversity and succession of magmatic events affecting the continental crust at the regional and global scales. This study reconstructs the evolutionary path followed by the crust segment today exposed in the eastern part of the French Massif Central (FMC), a portion of the Variscan belt of Western Europe, with the aim to investigate the potential flaws of the zircon record of crust evolution. In this scope, the origin and geodynamic significance of the constituent FMC lithological units are tackled by combining conventional petrological observations with zircon U-Pb-Hf-O isotope data. The results obtained following this integrated approach are then confronted to the conclusions that would have been drawn solely from zircon isotopic signatures, taken out of their petrological context, as is commonly performed in studies investigating crust evolution. The oldest rocks of the FMC correspond to Ediacaran (590_550 Ma) meta-sediments deposited in back-arc basins along the northern Gondwana margin. Such basins were fed by a mixed detritus originating from the adjacent Cadomian magmatic arc and a distal Gondwana source, presumably the Sahara Metacraton. Partial melting of these meta-sediments at the Ediacaran/Cambrian boundary led to voluminous S-type granitic magmatism, pinpointing a first major crust reworking event in the FMC. The origin of anatexis likely stems from the transient thickening of the hot, back-arc crust caused by the flattening of the Cadomian subduction. Subordinate melting of the depleted backarc mantle at that time is also documented. During the Lower Paleozoic, rifting of the northern Gondwana provoked coeval crust and (limited) mantle melting. Mantle-derived igneous rocks show markedly diverse trace element and isotopic signatures, consistent with a very heterogeneous mantle source pervasively modi_ed by the Cadomian subduction. Finally, the Variscan collision resulted in crustal melting as evidenced by the emplacement of S-type granites and the formation of migmatite domes, the spatial distribution of which being partly controlled by the crustal architecture inherited from pre-orogenic events. Synchronous intrusion of mafic mantle-derived magmas and their differentiates testify for Variscan post-collisional new continental crust production in the FMC. Two major inconsistencies exist between these results and the zircon record. First, zircon Hf model ages would point to substantial Mesoproterozoic crust formation in the FMC whereas more than 60% of the crust is actually Neoproterozoic in age. Second, new additions to the continental crust volume during the Variscan orogeny are not recorded even though 5 to 10% of the exposed crust formed at that time. The origin of both discrepancies inherently lies in the mixed isotopic signature carried by many zircon grains. Such equivocal information can only be detected when additional petrological constrains on the zircon host rocks are available and provide guidance in interpreting the zircon record of crust evolution
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Tectonostratigraphic evolution of the Swartland region and aspects of orogenic lode-gold mineralisation in the Pan-African Saldania Belt, Western Cape, South AfricaBelcher, Richard William 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The Swartland region in the western Cape, South Africa, covers approximately 5000
km2 and forms part of the Pan-African Saldania Belt that represents the
southernmost extremity of the Pan-African orogenic belts in southern Africa. Regional
mapping of the Swartland area shows that lithologies can be classified using
predominantly structural and to a lesser extent lithological criteria. This led to the
proposal of a new classification, were rocks of the previous classification of the
Malmesbury Group are divided into two new groups, namely the Swartland and
Malmesbury groups.
The Swartland group can be divided into the Berg River and Moorreesburg
formations, a series of quartz-chlorite-muscovite-feldspar schists, quartz schists,
graphitic schists and limestones; and the Bridgetown formation, a series of
metavolcanic rocks with WPB-MORB affinities that possibly represent seafloor.
Deposition of the sediments is suggested to have occurred concurrently with
deformation in an accretionary prism/fore-arc and was initiated with the opening of
the lapetus Ocean at ca. 600 Ma. This early deformation event, Dt (ca. 575 Ma), only
affected the Swartland group and exhibits pervasive bedding transposition, thrusting
and imbrication of units creating a tectonostratigraphic sequence. Where identified,
kinematic indicators and fold vergence indicate a top-to-the-west transport direction
during the early, low-angle Di deformation.
The Malmesbury group overlies the Swartland group, being locally separated by an
unconformity. The Malmesbury group is a succession of conglomerates, grits and
shales (Piketberg Formation), grading into greywackes, shales, siltstones,
sandstones and minor limestones of the Tygerberg and Porterville formations.
Sedimentation probably commenced after ca. 575 Ma and lasted until shortly after
560 Ma. Both the Swartland and Malmesbury groups were then deformed by the deformation event, D2 (ca. 552-545 Ma), and were intruded by the 552 to 510 Ma
Cape Granite Suite. The Franschhoek Formation, formally part of the Malmesbury
Group is now classified, along with the inferred ca. 535-510 Ma Magrug and
Populierbos Formations of the previous Klipheuwel Group. The redefined Klipheuwel
group documents a change in depositional environment from the continental
slope/ocean trench, marine and flyschoid deposits of the Malmesbury group to
continental, fluvial half-graben and graben deposits. Exhumation, extensive erosion
and the formation of a peneplain, was followed by the deposition of the Table
Mountain Sandstone Group around 550-510 Ma.
The Spitskop gold prospect, located 10 km south of Piketberg, represents the first
identified occurrence of mesothermal gold mineralisation in the Saldania Belt.
Metamorphic devolatilisation of the Swartland group during Di led to the scavenging
and transportation of gold along shallow-dipping shear zones that are contained
within the early, sub-horizontal So/Si tectonic fabric. Pervasive fluid movement in the
Spitskop area led to elevated gold values compared to background values
throughout the lithologies at Spitskop. The lack of any economic-grade gold
mineralisation is probably related to the absence of suitably orientated structures,
such as high-angle faults, that are commonly believed to represent the prerequisite
for large fluid throughputs that could result in economic-grade gold deposits. The
mineralisation at Spitskop, however, provides a genetic model for further exploration
of gold in the Swartland group. / AFRIKAANSE OPSOMMING: Die Swartland streek in die Wes-Kaap, Suid-Afrika, beslaan ongeveer 5000 km2 en
vorm deel van die Pan-Afrikaanse Saldania-gordel wat die mees suidelike deel van
die Pan-Afrikaanse orogene gordels in suidelike Afrika verteenwoordig. Regionale
kartering van die Swartland streek dui aan dat die gesteentes geklassifiseer kan word
deur oorwegend strukturele, en tot 'n mindere mate litologiese kriteria te gebruik.
Gevolglik word ‘n nuwe klassifikasie voorgestel, waar gesteentes volgens die vorige
klassifikasie van die Malmesbury groep verdeel word in twee groepe, naamlik die
Swartland en Malmesbury groepe.
Die Swartland groep kan verdeel word in die Bergrivier en Moorreesburg formasies,
‘n reeks kwarts-chloriet-muskoviet-veldspaat skis, kwarts skis, grafitiese skis en
kalksteen; en die Bridgetown formasie, ‘n reeks metavulkaniese gesteentes met
WPB-MORB affiniteite wat moontlik oseaanvloer verteenwoordig. Daar word
voorgestel dat afsetting van die sedimente gelyktydig plaasgevind het saam met
vervorming in ‘n akkresionere prisma/voorboog, geinisieer deur die opening van die
lapetus Oseaan (ca. 600 Ma). Hierdie vroee vervorming, Di (ca. 575 Ma), het slegs
die Swartland groep geaffekteer en vertoon deurdringende verplasing van
gelaagdheid, oorskuiwing en imbrikasie van eenhede en het ‘n tektonostratigrafiese
opeenvolging gevorm. Waar identifiseer, dui kinematiese aanwysers en plooi
kanteling op ‘n bokant-na-wes beweging gedurende die vroee, lae hoek Di
vervorming.
Die Malmesbury groep oordek die Swartland groep, plaaslik geskei deur ‘n
diskordansie. The Malmesbury groep bestaan uit ‘n opeenvolging konglomeraat,
grintsteen en skalie (Piketberg formasie), wat gradeer in grouwak, skalie, sliksteen,
sandsteen en ondergeskikte kalksteen van die Tygerberg en Porterville formasies.
Sedimentasie het waarskynlik begin na ca. 575 Ma en het voortgeduur tot kort na 560 Ma. Beide die Swartland en Malmesbury groepe is hierna vervorm deur D2, (ca.
552-545 Ma) en daaropvolgend ingedring deur die 552 tot 510 Ma Kaap Graniet
Suite. Die Franschhoek Formasie, voorheen deel van die Malmesbury Groep, word
nou geklassifiseer tesame met die afgeleide ca. 535-510 Ma Magrug en Populierbos
formasies as deel van die voorheen geklassifiseerde Klipheuwel groep. Die
hergedefinieerde Klipheuwel groep dui op 'n verandering in afsettingsomgewing
vanaf die kontinentale glooiing/oseaantrog, mariene en flyschoiede afsettings van die
Malmesbury groep na kontinentale, fluviale half-graben en graben afsettings.
Herblootstelling, omvattende erosie en die vorming van ‘n skiervlakte is gevolg deur
die afsetting van die Tafelberg Sandsteen Groep random 520-510 Ma.
Die Spitskop goudvoorkoms, 10 km suid van Piketberg, verteenwoordig die eerste
identifiseerde voorkoms van mesotermale goudmineralisasie in die Saldania Gordel.
Metamorfe ontvlugtiging van die Swartland groep gedurende Dt het aanleiding gegee
tot die roofuitruiling en vervoer van goud langs laaghellende skuifskeursones in die
vroee, subhorisontale S0/Si tektoniese maaksel. Deurdringende vloeistofbeweging in
die Spitskop omgewing het aanleiding gegee tot verhoogde goudwaardes in
vergelyking met agtergrond waardes dwarsdeur die litologiee by Spitskop. Die gebrek
aan ekonomiese graad goud mineralisasie is waarskynlik verwant aan die
afwesigheid van geskikte georienteerde strukture, soos hoe hoek verskuiwings, wat
oor die algemeen beskou word as ‘n voorvereiste vir die toevoer van groot
hoeveelhede vloeistof wat kon aanleiding gegee het tot ekonomiese graad
goudafsettings. Die mineralisasie by Spitskop verskaf egter 'n model vir verdere goud
eksplorasie in die Swartland groep.
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Analýza tektonického vývoje jednotky Královského Hvozdu / Structural evolution of the Královský Hvozd UnitVrtiška, Luboš January 2014 (has links)
5 English abstract The introduction of the thesis represents a profound research of current knowledge and survey results to date about the geodynamic tectonic boundary development of the Teplá- Barrandien unit/Moldanubian senzu stricto and the Královský Hvozd unit in the Šumava Mountains. It also describes in detail lithology of the Královský Hvozd unit and historical as well as contemporary opinions of the tectonometamorphic development of the Královský Hvozd unit and adjacent Moldanubian unit and Teplá-Barrandien unit. The research part of the thesis brings results of the analysis of the Královský Hvozd unit tectonic development in relation with the tectonic development of broader surrounding area. The research combines field structural data, detailed microstructure data acquired from collected samples and results of studying deformation mechanisms on orthogneiss samples from the Královský Hvozd unit using the EBSD (Electron Back Scattered Diffraction) performed on partly recrystalised quartz aggregates. The research output is a construction of a tectonic development model of the Královský Hvozd unit and the adjacent area. Four main deformation events (D1-D4) were determined on the basis of structural record and their time sequence in the rocks of the Královský Hvozd unit. On the basis of kinematic...
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Mineralogy and geochemistry of Late Archean and Paleoproterozoic granites and pegmatites in the Northern Penokean terrane of Marquette and Dickinson Counties, MichiganJohnson, Christopher M, Van Daalen, Christopher M 15 December 2015 (has links)
This thesis focuses on mineralogy, geochemistry, and origin of eight pegmatites and two spatially associated granites of Late Archean and Paleoproterozoic ages located in Marquette and Dickinson Counties, Michigan. Biotite geochemistry reveals that both granites and all pegmatites are peraluminous and have an orogenic signature. However, bulk composition reveals the Humboldt granite is a peraluminous A-type granite and the Bell Creek granite is a peraluminous mix between I-, S-, and A-type granites. The Republic Mine pegmatite appears to be geochemically similar to the Bell Creek granite and Grizzly pegmatite. The Crockley pegmatite is genetically related to the Humboldt granite. The Groveland Mine, Sturgeon River, and Hwy69 pegmatites appear to be a product of the Peavy Pond Complex being contaminated with the Marquette Range Super Group. Contamination and anatexis have made classification of the granites and pegmatites problematic. The Grizzly should be classified as a primitive LCT-type even though this pegmatite lacks characteristic enrichment associated with LCT pegmatites. Mineralogical geochemistry reveals that the Republic Mine is relatively more primitive than other pegmatites and should be classified as a primitive Mixed-type pegmatite. Groveland Mine has mineralogy and geochemistry not normally associated with NYF-type pegmatites and should be classified as Mixed. The Crockley pegmatite should be classified as NYF-type with a primitive LCT overprint. Dolfin, Hwy69, Sturgeon River, and Black River pegmatites should be classified as Rare Element, REE, NYF-type, although the Black River has slight tantalum enrichment expressed in columbite group minerals.
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Sedimentary and structural characteristics of the Triassic Nanpanjiang Basin (Southwest China). New insights on the regional tectonic evolution / Caractéristiques sédimentaires et structurales du basin triasique de Nanpanjiang (Chine du Sud ouest). Nouvelles perspectives sur son évolution tectoniqueXia, Wenjing 31 October 2018 (has links)
En tant qu'un des plus grands bassins sédimentaires du bloc de Chine du Sud, le bassin de Nanpanjiang a attiré une grande attention de la communauté géologique depuis de longtemps. Après plusieurs années de recherche, il reste encore de grand débats sur i) la provenance du bassin, ii) l'âge du changement de régime extension à compression, iii) le type de bassin et son contexte géodynamique. Dans cette thèse, nous avons conduit une étude pluri-disciplinaire incluant l'analyse des faciès sédimentaires et leur distribution géographique, paléocourants, spectres des minéraux lourds et leur geochimie, la géochronologie U-Pb sur zircon et baddeléyite, et le magnétisme des roches pour reconstrurier l'evolution de ce bassin. Les résultats indiquent un trois-étapes évolution. i) durant la période du Permien supérieur au début du Trias, la diabase mise en place 269Ma annonce l'ouverture du bassin, l'environnement sédimentaire est devenu plus profond. ii) durant la période du stade tardif du Trias inférieur (~ 245 Ma) au Trias moyen, à cause des influences de l'orogène Xuefengshan et de l'orogène d'Indochine situées à l'est et au sud du bassin, le bassin a évolué en bassin d'avant-pays. La diabase arrête sa mise en place durant cette période. Les analyses de détritus et de paléo-courants indiquent que durant cette période, les provenances de la partie est et de la partie sud du bassin étaient respectivement l'orogène Xuefengshan et l'orogène Indochinois. iii) la fin du Tirassique, la profondeur de l'environnement sédimentaire a fortement diminué, indiquant que le bassin a commencé à se rétrécir sous l'effet de la compression de l'orogène Xuefengshan et de l'orogène d'Indochine. / Ranks as the largest sedimentary basin in the South China during the Triassic, The Nanpanjiang basin attracts a large attention of the geology community for a long time. After many years study, there still exist several debates on i) the provenance of the sedimentary detritus, ii) the time of the change of the tectonic regime from extension to compression, iii) the type of the basin and its geodynamic background. In this thesis, a multidisciplinary study including analysis of sedimentary facies, paleo-current, frame work detritus mode, heavy mineral combinations and their geochemistry feature, rock magnetism and Zircon-baddeleyite isotopic dating on diabase was conducted to rebuild the evolution of the basin.The results show a three-stage evolution, i) during the Late Permian to the Early Triassic, the 269Ma diabase intruding into the basin announces the opening of the basin, the sedimentary environment became deeper. ii) During the late stage of the Early Triassic (~245 Ma) to the Middle Triassic, owing to the influences of the Xuefengshan orogen and the Indochina orogen which are located to the east and south of the basin, the basin evolved into a foreland basin. The diabase ceased emplacement in this period. The detritus and paleo-current analysis indicate that during this stage, the provenances of the East part and the South part of the basin were Xuefengshan Orogen and Indochina Orogen respectively. iii) During the Late Tirassic, the depth of the sedimentary environment decrease drasticly, indicating that the basin began to shrink owing to the compression of the Xuefengshan Orogen and the Indochina Orogen.
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Tectonic History and Present-Day Deformation in the Zagros Fold-Thrust BeltHessami, Khaled January 2002 (has links)
<p>This thesis uses various approaches such as observation of satellite images, field investigations, analogue modeling and GPS measurements to constrain deformation of the basement and sedimentary cover of the Zagros fold-thrust belt in time and space.</p><p>Focal mechanism solutions of most earthquakes indicate that deformation in the Zagros basement is due to shortening and thickening through numerous thrust faults. However, observations of strike-slip faulting recognized on satellite images imply that N-S trending faults in the Zagros, inherited from Pan-African basement, rotated about vertical axes to accommodate the convergence between Arabia and central Iran.</p><p>Field studies suggest that southwestward advance of the Zagros front has been recorded by syn-sedimentary structures. These structures indicate that deformation started as early as end Eocene in the northeast of the Simply Folded Zone and propagated progressively to the southwest. The deformation front drove the foreland basin to its present position along the Persian Gulf and Mesopotamia. </p><p>Scaled analogue models suggest that the seismicity due to orogenic shortening depends largely on the friction between the cover and its basement. Models show that fold-thrust belts with low tapers shortened above low friction ductile decollements involve several long-lived thrust faults generating low to moderate earthquakes over wide areas at the same time. By contrast, earthquakes with larger magnitudes are expected to occur along a few short-lived thrust ramps in fold-thrust belts with larger tapers shortened above high-friction decollments.</p><p>GPS-derived velocities across and along the Zagros suggest that only about one third (10 ± 3 mm/yr) of the current convergence between Arabia and Eurasia is accommodated within the Zagros by thickening to the east of the Kazerun Fault and thickening and lateral movement to the west. The remaining (21 ± 3 mm/yr) is transferred beyond the Zagros suture to central Iran and the northern Iranian mountains.</p>
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